Conventional electromagnetic motors generally require provisions for removal of heat. Heat is produced in electric motors and generators by electrical resistance and the sliding friction of slip rings, brushes, and commutators that transmit power between fixed and rotating structures. The conduction of even moderate currents through sliding contacts repeatedly welds and breaks the contacts, causing a continual rearrangement of conducting material. As a result, contact surfaces become rougher with continued use. Brushes, which have a relatively small contact surface area, generally wear out faster than rings. These characteristics of resistive heating, contact welding, and short lifetime of motor parts make conventional electric motors unsatisfactory in some applications and environments.
The limitations of electric motors in environments such as outer space has led to the investigation of alternative types of transducers, actuators, and motors. Piezoelectric devices, for example, have advantages of weight and efficiency that are important considerations for applications in space. Piezoelectric actuators have limited actuation speed, however, and known piezoelectric motors are not capable of high speed operation. Thus, there is a need for a high speed, high efficiency piezoelectric motor for performing work in severe environments and remote locations.